The present invention relates to a method for recovering component aromatic polycarbonate values, such as dihydric phenol and diarylcarbonate from scrap aromatic polycarbonate. The scrap aromatic polycarbonate is initially subjected to basic phenolysis. Dihydric phenol is then recovered as a dihydric phenol/phenol adduct, and diarylcarbonate is recovered by distillation of the resulting mother liquor.
Prior to the present invention as shown by Idel, U.S. Pat. No. 4,212,774, scrap polycarbonate was saponified in bulk in the presence of an aqueous alkali metal hydroxide solution to produce bisphenol A. The resulting mixture was thereafter phosgenated to produce a polycarbonate. Although polycarbonate made by Idel exhibited valuable mechanical and rheological properties, the product was often contaminated with organic additives which were not eliminated during the saponification and phosgenation stages. As a result, the physical properties of the recycled polycarbonate were often sub-standard. It would be desirable, therefore, to be able to depolymerize scrap polycarbonate to allow for the recovery of basic polymer forming ingredients, such as readily purifiable bisphenol A and diphenylcarbonate. These basic ingredients can be converted to polycarbonate by standard melt-transesterification procedures; the resulting polycarbonate has substantially the same physical properties as virgin polycarbonate source material.